Hot oils or fats are often used not only once, but utilized in deep fryers over a longer period for successively preparing different foods. The oil or fat is decomposed by oxidation at the hot operating temperatures between approximately 120° and 180° C. and undesirable chemical products such as free fatty acids and polymers are formed, which do not only impair the taste, but may also have adverse health effects.
In order not to replace frying oils or fats too early or too late, measuring devices are used for measuring the state of oils or fats, including tests for their electrical properties. Measuring the dielectric constant, which is a reliable measure of the degree of decomposition of the fat or oil, is particularly suitable.
EP 1 046 908 A2, for example, describes a measuring device for measuring the state of an oil or fat, which has a housing which contains the electronic analyzing units and a data display, as well as a tubular connecting element with a sensor situated at its tip which may be directly immersed into the hot oil or fat and is suitable for determining the dielectric constant. The sensor and the electronic analyzer circuit are electrically connected via a cable laid freely within the connecting element.
DE 101 63 760 A1 describes a refinement of the above-mentioned measuring device. In the measuring device presented therein, the electrical conductors between sensor and electronic analyzer circuit are formed by metallic conductors printed on a ceramic substrate. The tubular connecting element is shaped in such a way that it surrounds most of the substrate and narrows downward so that only the area of the substrate on which the sensor is situated is accessible from the outside. An insulating sealing adhesive is introduced and cured between substrate and connecting element, so that there is no electrical connection between the connecting element and the electric conductors. In addition, a temperature-stable seal is thus achieved, which prevents the oil from penetrating inside the connecting element. A temperature sensor may also be provided, whose measurement results may also be processed by the electronic analyzer circuit.
The disadvantage of this device is, however, that heat is transferred from the oil or fat to be measured to the electronic analyzer circuit and thus the service life of the components is reduced and/or the accuracy of the measurement results is impaired.
Accordingly, it is desirable to provide a measuring device that would significantly reduce the temperature load on the electronic analyzer circuit and thus increase the service life of the electronic components.